1. Field of the Invention
The present invention relates to a method for growing a single crystal thin film of an element semiconductor and more specifically to a method suitable for growing a high-quality single crystal thin film of an element semiconductor with the precision of a monomolecular layer. 2. Description of Prior Art
As epitaxy techniques for the formation of an epitaxially grown single crystal layer of an element semiconductor consisting solely of one element such as silicon, there have been heretofore known, for example, chemical vapor deposition hereinafter referred to as "CVD"), molecular beam epitaxy (hereinafter referred to as "MBE"), etc. Further, recently, one of the Inventors (Junichi NISHIZAWA) proposed a molecular layer epitaxy method (hereinafter abbreviated as "MLE") which made possible the formation of a grown single crystal layer with the precision a monomolecular layer by alternately introducing different kinds of gases. (Japanese Patent Application No. 59-153978 which has been laid open to public inspection as Laid-Open No. 61-34928.)
However, the above-mentioned known methods have not been completely satisfactory because of the disadvantages set forth below.
For example, in CVD, a source gas (e.g., SiH.sub.4) is introduced simultaneously with a carrier gas (e.g., hydrogen) into a reaction chamber and then single crystals are grown by pyrolysis. In a such manner, contamination by impurities is apt to occur due to the introduction of the carrier gas, thereby causing not only deterioration of the quality of a grown layer, but also other problems, for example, difficulties in controlling with the precision of a monomolecular layer.
On the other hand, in the case of MBE in which crystal growth is carried out under ultrahigh vacuum, it is difficult to maintain the rate of crystal growth constant over a long time. Further, MBE is still inferior in the quality of the resulting crystals as compared to CVD set forth above.
MLE has been developed with the object of overcoming the disadvantages of these former methods, but this method is disadvantageous in that the gas feeding system is complicated, since different gases are repeatedly alternately fed. Therefore, improvement has been awaited.